Wet and Dry Stormwater Ponds

A pond is a type of stormwater management facility designed to collect rainwater and pollutants and prevent downstream flooding.

Wet ponds always have a pool of water.
Dry ponds only have water after rain.

Ponds have an embankment (called a dam) to hold back water that is entering the pond. Most dams are earthen (not concrete) and are grass covered. All stormwater ponds also have a control structure that releases water at a much slower rate than the stormwater entering the pond. While water remains in the pond, pollutants have time to settle at the bottom.

Most ponds located throughout Montgomery County are stormwater management ponds, even ones that are community amenities. Ponds can have many different designs, including ponds with concrete channels, dry ponds with sand filters on the pond bottom, and ponds that provided wetland habitat around the edges.

Why are Stormwater Ponds Important?

Stormwater ponds are important stormwater management tools, because they:

Remove pollutants
Improve health of streams and rivers
Help to make our waters fishable and swimmable
Improve the quality of the Chesapeake Bay

As rainwater flows over hard surfaces and lawns it picks up pollutants such as sediment, trash, pesticides from lawns, nutrients from fertilizer or pet waste, and oil and grease from cars. Ponds can help to reduce this pollution from entering our waterways.

Maintaining Your Stormwater Ponds

As the property owner, you are responsible for all maintenance of your stormwater pond unless a shared maintenance agreement has been made with the DEP Stormwater Facility Maintenance Program. Ponds at County facilities and schools are the maintenance responsibility of the Department of Environmental Protection. Maintenance of ponds in County parks is shared between DEP and M-NCPPC.

Stormwater ponds require regular maintenance similar to other landscaped areas, including grass cutting, trash removal, and vegetation management. Please visit the stormwater facilities maintenance page for a list of approved contractors. Utilizing the services of DEP-approved contractors is required for structural maintenance and is recommended, but not required, for non-structural maintenance.

Un-maintained ponds may:

Not remove pollutants as intended, sending polluted water to streams and rivers
Become filled with sediment and debris, so water cannot be stored in the facility, which may lead to downstream flooding and erosion
Look unsightly with excessive growth of unwanted weeds or algae
Cost more to fix problems if left unchecked
Lead to a dam breach if overgrown vegetation and trees compromise the pond safety over time. This would cause flooding and damage to surrounding properties and adjacent homes
Have inlet and outlet areas blocked by excessive growth or debris. This will cause water to back up or pond on adjacent properties

Graphic of a pond and suggested location for performing maintenance.

By maintaining your stormwater pond, you are doing your part to help the environment and protect your local streams and the Chesapeake Bay.

How Will I Know What Maintenance is Required?

Montgomery County regulations require that you perform ongoing routine grass cutting, trash removal, and vegetation management of your stormwater facility. If the work described below is not done regularly, you could receive a notice of violation.

Grass Cutting

✔ Mow grass in the pond area at least twice a year

Downstream slope of dam
Top of the dam
Upstream slope of dam (dry pond only)
25 feet around the control structure (dry pond only)
Inlet channels, around headwalls, and pipes within pond area (where safe and accessible)
Outlet channel

Vegetation Management

✔ Manually remove all trees and woody vegetation in the following pond areas at least twice a year

From the top and upstream and downstream slopes of the dam
From inlet and outlet channels
Within 25 feet of the control structure
From channels, headwalls, and pipes into the pond area

✘ Do not apply herbicides, fertilizers, or pesticides in or around the pond. If manual removal of invasive weeds has been ineffective, limited applications of aquatic friendly herbicide may be applied by a qualified professional certified by the State of Maryland. The Maryland Department of Agriculture (MDA) is the licensing body and they have a web tool where you can enter a name of a company to find out if they are licensed.

The most commonly forgotten non-structural maintenance is mowing and removal of trees and woody vegetation on the downstream slope of the embankment.

Trash Removal

✔ Remove trash and debris from all areas in and around the pond monthly

For wet ponds, any trash in the water should be removed safely by professionals

Other Preventive Maintenance

As needed:

✔ Know the pollutant sources on your property and try to reduce or eliminate the pollutants at the source

✔ Notify DEP if beaver activity or animal burrowing is observed

✔ Prevent trees and woody vegetation from growing in the areas mentioned above in the Vegetation Management section

✔ Seed and cover adjacent areas of bare soil to prevent erosion

✔ Notify Montgomery County police if graffiti is observed

✔ Verify all pond safety signs are in place

✔ Inspect the facility after every major storm and contact DEP if you are concerned

These basic actions will keep your facility working correctly and prevent more serious repairs, which will save you money in the long term.

Image of the front of the Non-structural Pond Maintenance Fact Sheet.

Need Help with Basic Pond Maintenance and Troubleshooting?
Download the Fact Sheet ( PDF, 1.54MB)

Structural Maintenance

Structural maintenance must be performed by contractors who have been approved by DEP . No one should remove control structure manholes or enter the control structure without proper training, certification, and permits for confined space entry. Entering the water or any confined spaces without these requirements is a violation of State law and could be dangerous or deadly.

Structural Maintenance Issues

Missing pond safety sign
Accumulation of sediment and debris within the ponds
Damaged or corroded trash racks
Shoreline erosion on the dam embankment
Dry pond holding water longer than 72 hours
Damaged or clogged inlet and outlet channels, pipes, and trash racks
Leaking control structures and pipe joints
Cracks or damage to the concrete control structure

Serious Failures
(Require immediate attention! Notify DEP as soon as possible)

Cracks or sink holes on the dam embankment
Beaver lodges in the wet pool blocking outlet pipes
Damaged or broken control structure
Animal burrows in the dam embankment
Slope failure on the dam embankment
Missing manhole covers on the control structure

Image of the front of the Structural Pond Maintenance Fact Sheet.

Want Help with Pond Structural Maintenance?
Download the Fact Sheet ( PDF, 1.07MB)

Ponds in the Stormwater Facilities Maintenance Program

The Stormwater Facilities Maintenance Program is responsible for maintaining all public stormwater facilities as well as all private facilities that transferred their maintenance to the County. The program also maintains facilities that were required as part of the Department of Planning permits.

Not sure if your stormwater pond is part of the Stormwater Facilities Maintenance Program?

Check out online Facilities Map or email askdep@montgomerycountymd.gov .

Image of a man mowing around a stormwater pond.

Can I remove my stormwater pond after installation?

No, you cannot remove any facilities that were part of your building installation - these are permitted structures and DEP maintains a database of these facility locations as part of the Stormwater Facility Maintenance Program. DEP will perform a maintenance inspection of your practice if it is a permitted structure. Property owners must contact DEP before any major changes can be performed to the structure.

Pond Safety and Concerns

Mosquitoes

Stormwater management facilities are often blamed for large numbers of mosquitoes, because the facilities contain rainfall runoff. But when a stormwater management facility is designed and maintained properly, it should not contribute to excessive mosquito populations.

DEP has developed a webpage and brochure with all the information you need to identify if mosquitoes are coming from a mal-functioning stormwater management facility and how to prevent these issues. The webpage also contains general information on mosquito biology and prevention. Visit the DEP Mosquitoes webpage

Signs and Fencing

The Montgomery County Code, Chapter 19, Article II, Section 19-28(d)(2), Inspection and Maintenance of Stormwater Management Systems requires the Montgomery County Department of Environmental Protection (MC DEP) to inspect fences or safety devices. When a deficiency is discovered, MC DEP must require property owners to correct the deficiency.

The Montgomery County Code, Chapter 36, Pond Safety states that any publicly accessible pond must have warning signs posted on all sides of a pond and at any major approach to the pond, such as a path; if not surrounded by a continuous, permanent fence or barrier.

Pond Signage

The Montgomery County Code (section 36-3) requires that a person who owns or controls land that includes a publicly accessible pond must post warning signs around the pond and at any major approach to the pond, such as a path. A publicly accessible pond is defined as a water impoundment that:

Retains a permanent pool more than 24 inches deep and 20 feet across at its widest point
Is not a swimming pool as defined in Chapter 51 of the Montgomery County Code
Is not surrounded by a continuous, permanent fence or barrier (at least 4 feet high with no opening wider than 2 inches) within 100 feet of the shoreline

The County Code has established standards for warning signs, including the size, message, construction, placement, and maintenance. They are listed in the table below.

Standards for Pond Safety/ Warning Signs

Placement

Warning signs must be posted on all sides of a publicly accessible pond and at any major approach to the pond, such as a path.
Warning signs may be posted in the pond or on the shore.
Warning signs must be visible from the shore and not obscured by vegetation or other obstructions.
Warning signs at golf courses may be posted at the main entrance to the golf course rather than at each pond.

Size

Warning signs must be at least 18 inches high by 24 inches wide.
The lettering on warning signs must be at least 2 inches high, and any graphics must be large enough to be clearly seen.

Construction

Warning signs must be made of a weather-resistant material such as metal, pressure-treated wood, plastic, or an approved equivalent.
All lettering, graphics, and the surface of the sign must be composed of a weather-resistant material.
The sign must be securely anchored.

Message

The warning sign must, at a minimum, warn that entering the water to swim, skate, or boat is unsafe. The sign may use the international symbols for prohibited activities.
The sign must provide a legible written message and appropriate graphics.

Maintenance

Warning signs required under Chapter 36 must be maintained in good condition by the person who owns or controls land that includes a publicly accessible pond.

Fences Around Ponds

The Montgomery County Code does not require fences to be installed around ponds. However, if fences exist around a pond or elsewhere as part of a stormwater management facility, fences shall be inspected and maintained in a manner acceptable to DEP.

The Montgomery County Code, Chapter 19, Article II, Section 19-28(d)(2), Inspection and Maintenance of Stormwater Management Systems requires the Montgomery County Department of Environmental Protection (MC DEP) inspect fences or safety devices. When a deficiency is discovered, DEP must require property owners to correct the deficiency.

The County Code has also established standards for fences, including permissions/permitting, location, construction, and plan submission.

Standards for Fences around Ponds

Permissions and Permitting

The erection of fences across and/or through public easements and/or rights-of-way requires permission from the easement and/or right-of-way owner. Contact MC DEP for more information on obtaining required permissions.
All fences require a signed and recorded Declaration of Covenants (Available in Guidance Doc).
All fences require a building permit from the DPS.
Any fence erected within the 100 year floodplain requires a Floodplain District Permit from DPS.

Location

All fences shall be erected to completely surround the pond, storm drain out falls into the pond and the riser structures, except as may be noted here.
- Generally, fences shall be erected two feet from the inside edge of the “bench” where provided.
- Adequate clearances shall be maintained between any fence and riser.
Gates shall be provided for maintenance access.
- A twelve foot (12’) minimum wide double gate shall be provided across the maintenance access; and,
- A three foot (3’) minimum wide single gate shall be provided behind the riser structure.
- All gates shall be padlocked.
For ponds where an emergency spillway exists, fences cannot be across the emergency spillway.
Fences shall not be constructed across such creeks streams channels and other open drainage-ways. Fences she'll be terminated at the “top of bank” at all creeks, streams, channels and other primary open drainage-ways.
Where fences are terminated at creeks, streams, channels and other open drainage-ways, a metal sign that reads: STORMWATER MANAGEMENT AREA NO TRESPASSING must be erected.

Construction

All fence shall be chain link fence with a minimum height of forty-eight inches (48”) and comply with the latest edition of MSHA Standard Specifications Section 912.
- Chain link fence fabric shall be two inch (2”) mesh woven from galvanized wire minimum gauge #9.
Alternative fence types: The County will review requests for an alternate type of fence. Where approved, pressure treated split-rail fence with welded wire mesh may be substituted for a chain link fence.
- Split-rail fence shall have a minimum of three (3) rails, equally spaced. A minimum height of forty-eight inches (48”) shall be provided from finished grade to the top of the rail. Spacing between fence posts shall not exceed ten feet (10”).
- Welded wire fence used in conjunction with all split-rail fence must be vinyl coated, fourteen (14) gauge, forty-eight inches (48”) in height with openings no greater than two inches (2”) in width and four inches (4”) in height. Welded wire fencing must be firmly attached to the outward side of the split rail fence and the two inch (2”) dimension of the wire fence must be perpendicular to the fence post.

Plan Submission

Fences shall be shown on all as-built plans at the following locations:
- Plan view of Pond, and
- Included in the profile of the principle spillway.

Resources and Financial Incentives

Have a stormwater pond on your property? Financial incentives are available for you.

The Water Quality Protection Charge Credit Program

If you are responsible for structural maintenance and have maintained your stormwater pond, you are eligible to receive a credit off your annual Water Quality Protection Charge (found on your yearly property tax bill). The credit provides an incentive for maintaining your stormwater pond and other stormwater management practices. You must apply for the WQPC credit separately – the credit will not be provided to you automatically.

Choose your property type to learn more:

A dry pond with a sand filter on the bottom.